1. Field of the Invention
The present invention relates generally to an optical disk apparatus, and more particularly to optimization of recording power.
2. Description of the Related Art
In optical disk apparatuses capable of recording data on a media like a CD-R (compact disk-recordable) disk, optimization of recording power using a process referred to as “OPC” (optimum power control) is commonly performed. In OPC, test signals are written onto a predetermined recording area of an optical disk while recording power is varied among a plurality of levels over a corresponding-number of frames, for example, 15 levels over 15 frames, and the test signal are reproduced for evaluation of a signal quality. As a measure of quality of a reproduced signal, usually a β value is used. β value is a parameter calculated using the equation β=(A+B)/(A−B), where A and B are peak and bottom voltages of the envelope of the reproduced RF signal, respectively. When this β value so obtained is within a predetermined range (for example, 0.04 to 0.05), the recording power is determined as optimum. Then, the recording power by which a desired β value (target β value) is produced is selected as the optimum recording power, and later data recording operations are performed at this optimum recording power.
Japanese Patent Laid-Open Publication No. Hei 7-85494 discloses a technique for obtaining an optimum recording power comprising steps of determining two β values which are lower and higher than a desired β value respectively, predicting an expected recording power level by which the desired β value will be obtained based on a calculation using the lower and higher β values, and setting the power level closest to the expected level as an optimum recording power.
However, because any of a variety of optical disks can be used for recording, the target β value varies accordingly. It is possible to select the optimum recording power using a predetermined default β value, however, this does not necessarily provide an optimum recording quality. In some cases, a recording power is determined based on a β value higher than the substantially optimum β value. This can cause thermal waveform distortion of an RF signal such that it becomes impossible to reproduce that signal.
An optical disk usually has a unique disk ID prerecorded thereon, and thus it is possible to calculate a target β values for each disk ID and store the resultant target β value into a table held at the optical disk apparatus side. However, the associated process is very complex. In addition, this method does not addresses situations where a user attempts to record on an optical disk for which a target β value has not been stored.